The invention relates to a coupling for a belt tensioner in a vehicle comprising an input element, an output element, a coupling element which is movably supported on the input element between an initial position and an activated position and in the activated position couples the input element to the output element, and a control element which upon movement of the input element relative to the output element moves the coupling element between the initial position and the activated position.
Reversible belt tensioners include a drive adapted to be coupled to the retracting axle of a belt reel by means of a coupling. In regular operation of the belt retractor the belt reel is uncoupled from said drive so that unhindered winding and unwinding of the webbing onto and, resp., from the belt reel is possible, in the case of tensioning the drive is coupled to the belt reel via the coupling so that the webbing can be wound onto the belt reel and thus can be withdrawn.
A coupling for such belt tensioner is illustrated in DE 10 2011 119 343 A1, for example. The coupling substantially consists of an input element in the form of a disk which is permanently coupled to the drive, an output element coupled to the belt reel and a coupling element adapted to couple the input element to the output element. Further, there are provided a control element for moving the coupling element upon movement of the input element relative to the output element into an activated position in which the input element and the output element are coupled as well as a control lever adapted to fix the control element in a stationary manner.
In the case of tensioning the input element is moved and thus rotated by the drive. The control lever engages in the control element, for example a control disk, and maintains the same fixed so that the driven input element is displaced along with the coupling element relative to the control element. In this way, the coupling element is moved into the activated position in which the input element and the output element are coupled.
In order to uncouple the input element from the output element, it is required to control the drive so that it rotates into the opposite direction and, by moving the control element toward the input element, the coupling element is moved back to the initial position again.
This requires a drive that is adapted to rotate the input element into two opposite directions as well as a control which is controlled by the direction of rotation of the drive and of the input element.